Third Generation Partnership Project (3GPP) has defined a functionality called Access Network Discovery and Selection Function (ANDSF) specified in 3GPP Technical Specification (TS) 23.402 and 3GPP TS 24.312. This functionality is based on that the network provides the user equipment (UE) with policy rules for helping the user equipment in performing Wireless Local Area Network (WLAN/Wi-Fi) access selection and traffic steering.
Furthermore, the ANDSF mechanism is enhanced in 3GPP Rel-12 by addition of support for HotSpot (HS) 2.0 parameters as defined by Wi-Fi Alliance. The support for HS2.0 is specified in 3GPP Technical Report (TR) 23.865.
At the same time, there are ongoing enhancements to ANDSF in 3GPP Technical Specification Group (TSG) System Aspects (SA) 2. There is also an ongoing study in 3GPP TSG RAN2 on introducing Radio Access Network (RAN) support for controlling WLAN access selection and traffic steering. A motivation for introducing RAN support for this includes the possibility to make the access selection dependent on radio performance and radio network conditions such as signal strength, cell load etc.
Access Network Discovery and Selection Function
In the following, different components of ANDSF, as described in 3GPP TR 23.865 v12.0.0, are briefly summarized.
WLAN Selection Policy
The WLAN Selection Policies (WLANSPs) provide priorities between different WLANs. WLANSP cannot say anything about 3GPP cellular connections. It has been suggested to introduce Base Station System (BSS) load in the WLANSP polices which could then look like the example below.
With a policy like in the example, the user equipment would connect to WLAN A if in coverage and the load is below 70%, otherwise it would connect to WLAN B, if in coverage.
TABLE 1WLANSP example.Prio 1.WLAN A if Base Station System(BSS) load < 70%Prio 2.WLAN B
Inter-System Routing Policy
Inter-system routing policies (ISRPs) are used to indicate how the user equipment should route traffic between different accesses. ISRP is only applicable for UEs which are capable of having simultaneous connection to WLAN and 3GPP. The ISRP policies do not tell the UE which access to connect to but only how to route traffic once the UE is connected to the accesses simultaneously.
An example policy is found below. With the example policy the UE would route voice traffic to 3GPP but browsing to WLAN, if connected to both. If the UE is not connected to WLAN then the UE would route both voice and browsing over 3GPP.
ISRP Example.
                For Access Point Name (APN) A (e.g. voice):                    Prio 1. 3GPP            Prio 2. WLAN                        For APN B (e.g. browsing):                    Prio 1. WLAN            Prio 2. 3GPPRAN Controlled WLAN Offloading                        
In the 3GPP TSG RAN2 study on WLAN access selection, there is currently a proposed compromise solution, in which the user equipment performs access selection according to rules specified in RAN specifications. These rules indicate when the user equipment should go to WLAN and when the user equipment should go to 3GPP. According to the rule, the user equipment compares measured metrics, e.g. 3GPP and WLAN signals strengths, with thresholds signalled from RAN. In this document, these rules may be referred to as “RAN rules relating to WLAN”.
Example of RAN Rule for Long Term Evolution (LTE):
if (measuredRsrp < threshRsrpLow) AND (measuredRcpi >threshRcpiHigh) {   goToWlan( );} else if (measuredRsrp > threshRsrpHigh) OR (measuredRcpi <threshRcpiLow) {   goTo3gpp( );}
When the UE's measured Reference Signal Received Power (RSRP) is below threshRsrpLow and the measured received channel power indicator (RCPI) exceeds threshRcpiHigh, the user equipment would go to WLAN. When the UE's measured RSRP exceeds threshRsrpHigh or the measured RCPI is below threshRcpiLow, the user equipment would go to 3GPP.
The RAN will also indicate which WLANs should be considered by the user equipment when evaluating the RAN rule. This could for example be a list of WLANs provided to the UE. It is also be possible to have different RAN-lists for different sets of thresholds to provide WLAN distinction if seen necessary.
The known solutions for RAN/WLAN integration, or inter-working, gives the possibility for controlling Wi-Fi access selection and traffic steering based on radio performance, load, mobility and other parameters which leads to optimized end user and system performance. A problem is however is that there are scenarios when RAN control is not desired, e.g. when there is some other reasons for Wi-Fi selection which may not be controlled by the RAN.
A first exemplifying scenario relates to when the user equipment is roaming in another country. In this scenario, an operator typically wishes the user equipment to connect only to certain WLAN APs for which there is a special roaming agreement (lower cost). The operator policies for Wi-Fi selection may in this scenario be handled by ANDSF polices of a home operator relating to the user equipment, i.e. the subscription of the user equipment.
A second exemplifying scenario relates to when a user of the user equipment wishes to connect to a private network, over which the operator has no control. The policies for Wi-Fi selection may in this scenario be handled by end user preferences configured in the user equipment.